Insertable waveguide termination



p 1961 E. H. WINKLER INSERTABLE WAVEGUIDE TERMINATION 2 Sheets-Sheet 1 Filed May 15, 1960 INVENTOR. ERIC H.W|N LER Sept. 19, 1961 E. H. WINKLER INSERTABLE WAVEGUIDE TERMINATION Filed May 13, 1960 2 Sheets-Sheet 2 (I I Q 26 F I G 5 F I G 6 INVENTOR.

ATTO

The invention described herein may be manufactured and used by or for the United States Government for government purposes without payment to me of any royalty thereon.

This invention relates to a radio frequency (RF) dummy load for use in the termination of waveguide type transmission lines and, more particularly, to a lossy wall type dummy load which is directly insertable into the terminal end of a waveguide transmission line and operates to dissipate the microwave energy passing through the waveguide.

The design of RF dummy loads which do not require external power for their operation falls into two general types. The first type includes those dummy loads in which the electromagnetic field passes into a lossy or dissipating material which completely fills the volume of the waveguide. A second and more widely used type of dummy load is one in which the electromagnetic field passes through a section of waveguide which uses a layer of lossy material as a lining for the Waveguide wall. The present invention concerns improvements of the latter design.

In order to keep the voltage standing-wave ratio VSWR) at a minimum, dummy loads which are matched to the waveguide being terminated are generally used. These include the type in which the lossy wall material is formed Within a metallic housing. This housing includes a flange which is the means of attaching the dummy load to a mating flange on the waveguide of the electronic equipment being tested. The use of the conventional flange attachment requires that a section of waveguide be removed in order to insert the dummy load. Normally, the removed section would include the antenna horn which may be awkward to handle and located in a relatively inaccessible position.

Accordingly, it is an object of the present invention to provide a dummy load which can be easily inserted into the electronic equipment waveguide without disassembling or substituting sect-ions of waveguide.

Another object of the invention is to provide a dummy load which is simple and easy to construct and lighter in weight, thereby making it more useful in airborne equipment application.

Still another object of the present invention is to provide a dummy load which is small and compact and yet capable of dissipating relatively large amounts of microwave energy without excessive heating and without requiring fins or other heat dissipating accessories.

A further object of the invention is to provide a dummy load which is characterized by minimum reflective properties and voltage standing-Wave ratio.

These and other objects, features and advantages will become more apparent from the following description taken in connection with the illustrative embodiment in the accompanying drawings, wherein:

FIGURE 1 is a cross-sectional view of the terminal end of a waveguide including the antenna horn with the dummy load inserted therein;

FIGURE 2 is a view in perspective of a dummy load which embodies the present invention;

FIGURE 3 is a detailed cross-sectional view of the dummy load;

FIGURE 4 is a cross-sectional View of a second embodiment of the present invention attached to an antenna horn;

3,001,152 Patented Sept. 19, 1961 FIGURE 5 is a view in perspective of the second embodiment; and

FIGURE 6 is a detailed cross-sectional view of the second embodiment ready for insertion into a waveguide section.

Referring to the drawings, the terminal end of a waveguide antenna system is shown in cross-section in FIGURES 1 and 4. A curved section of conventional waveguide transmission line 13, having a rectangular crosssection, is terminated by an antenna horn 15. Mating flanges 17 are attached to the adjacent sections of the waveguide including the input end of the antenna horn 15. The flanged sections are generally bolted together by bolts 19 which pass through the flanges 17.

The conventional antenna horn generally includes a straight throat section 21 at its input portion and a horn portion 23 for controlling the direction. of the output of the electronic equipment to which it is attached. The present invention is concerned with terminating and dissipating the output of the equipment before it reaches the antenna horn 15. For this purpose, dummy loads, designated generally by the character reference numerals 25 and 26, may be inserted into the straight throat section 21 of the antenna horn 15.

A detailed view in perspective of a dummy load 25 designed according to the present invention is shown in FIGURE 2. A mould or form of a conventional lossy material 27 comprises the main portion of the dummy load. Imbedded at various positions in the outer wall of the form 27 are a series of metallic contacts 29 which extend a minimum distance beyond the outer surface of the dummy load. Also imbedded in the lossy material of form 27 near its input end are metallic strips 31 which provide a matching section and make contact with the walls of the section 211 at the point near the flange 17. It will be noted that the input end of the dummy load has a gentle sloping section 33 which extends from the leading edge of the lossy material to the straight wall of the dummy load. The angle of the slope 33 is determined by the dimensional configuration of the various waveguide sections, as well as the design requirement to effect a minimum discontinuity from the standpoint of voltage standing-wave ratio and peak power are over.

The wall thickness and cavity shape of the dummy load is based on known design criteria. The form or mould 27 is preferably fabricated from a ceramic type material with a fired glazed seal.

A metal flange 35 which serves as a stop is imbedded in the outer end of the dummy load 25. This flange 35 acts as a stop to limit the distance to which the dummy load may be inserted into the waveguide and also acts as a shield to prevent leakage and radiation effects. A handle 37 is provided to facilitate insertion and removal of the dummy load, particularly after it has been in use and has consequently reached an elevated temperature.

The relative dimensions of the cavity 39 of the dummy load 25 are dependent on the characteristics of the waveguide and microwave energy passing therethrough. The load should be designed to obtain a uniform power dissipation on all four walls throughout the length of the dissipation section. The design formulae published in Technique of Microwave Measurements, by Montgomery, vol. 11, in the MIT. Radiation Laboratory series, pp. 735 to 743, define the nature of the two-stage taper which has optimum dissipating qualities and a minimum voltage standing-wave ratio.

A detailed view in perspective of a second] embodiment of the insertion of the dummy load 26 is shown in FIG- URE 5. This embodiment is particularly adaptable for use with a pressurized Waveguide system and comprises a thin metal shell 41 in the form of a waveguide. The

exact size of the shell depends upon the waveguide size and known dummy load design criteria. A thin coating of lossy material 43 is applied to the inside surface of the shell 41. The lossy material 43 may be a relatively thin layer of ceramic or porcelain enamel fired or applied in such a manner that it adheres to the shell 41 as though it were an integral part thereof. This arrangement improves the heat conductivity and structural characteristics and provides a better and more easily obtained impedance match, hence improved voltage standing-wave ratio with less tendency for arc-over at the entrance opening as compared to other presently known loads.

A stop 45 in the form of a fiange is provided on the outer end of the load 26 and serves to limit the distance which the dummy load can be inserted into the waveguide section. An angle member 47 is attached to the stop 45 and serves to retain a pressurization seal 49 for use when the load is used in conjunction with pressurized waveguide systems. The seal 49 may be fabricated from a temperature resistant material which has rubber-like properties when inserted into the waveguide section. A handle 51 is provided for inserting as well as extracting the heated load after use in the system.

A series of metallic contacts 53 are attached at various positions on the outer surface of the shell 41 and are dimensioned to provide positive contact with the waveguide. These contacts 53 extend a minimum distance beyond the outer surface of the shell 41 consistent with the dimensional tolerances of the various size waveguides. The dimensions of the contacts 53 also depend upon the voltage standing-wave ratio requirements and minimum RF leakage considerations. For these reasons, it is most desirable that the contacts 53 extend fully across the outer surface of the load with suitable arrangements at the corners to prevent arc-over and RF breakdown, yet not binding each other or at the inside corner radius of the waveguide section.

At the entranceopening of the dummy load the metallic strips 55 are provided to form a gentle slope for guiding the microwave energy into the load 26. The strips 55 also contact the inner surface of the waveguide section and are dimensioned so as to be depressed slightly when inserted thereinto.

The application of the invention for terminating a waveguide transmission line is accomplished by inserting the dummy load into the antenna throat 21 or some straight portion of waveguide section. The metallic contacts 29 or 53 make positive contact with the inner wall of the waveguide and extend fully across and into the corners of the waveguide section. This arrangement serves to prevent arc-over and RF leakage past the load. It can be seen that this procedure is considerably simpler and more efiicient than the conventional method requiring disassembly of the waveguide system at the antenna horn or some other 'part of the electronic set-up and substituting a flanged dummy load for the removed part.

Although only certain embodiments of my invention have been described herein, it will be apparent to those skilled in the art that various changes may be made in the construction and size of the elements without departing from the spirit and scope of the invention as defined in the appended claims. For example, although the description of the invention has been directed toward a dummy load for dissipating microwave energy, the principle of the invention can be applied equally as well to the design of attenuators and other microwave accessories.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent in the United States Patent Office is:

1. A dummy load for insertion into a waveguide transmission line, said dummy load comprising a hollow structure of lossy material, and a plurality of fiat metallic contacts extending from the outer surface of said struc ture for contacting the inner surface of said waveguide transmission line, said hollow structure with the contacts extending therefrom being dimensioned to be sliditbly insertable into a section of waveguide transmission 5 inc.

2. A load as defined in claim 1 wherein said contacts have an end imbedded in said lossy material.

3. A dummy load as defined in claim 1 wherein said contacts are secured in a fixed relationship by their attachment to a sleeve mounted over said structure.

4. A dummy load for insertion into a waveguide transmission line, said dummy load comprising a hollow structure of lossy material having an entrance opening therein, a metallic strip surrounding said entrance opening and forming a gently sloping area, and a plurality of metallic contacts on the outer surface of said structure for contacting the inner surface of said waveguide transmission line, said hollow structure being dimensioned to he slidably insertable into a section of waveguide transmission line.

5. An insertable waveguide transmission line load for dissipating microwave power, said load comprising a hollow mould of lossy material having an entrance opening for receiving microwave power, and a plurality of metallic contacts imbedded in said mould of lossy material and extending beyond the outer surface thereof, said metallic contacts being dimensioned to contact and extend fully across a section of the inner wall surface of the waveguide transmission line to prevent arc-over and RF leakage.

6. The waveguide transmission line load defined in claim 5 wherein the hollow mould of lossy material includes a cavity having walls of two-stage tapered configuration.

7. An insertable waveguide transmission line load for dissipating microwave power, said load comprising a hollow metallic shell having an entrance opening for receiving microwave power, a coating of lossy material disposed on the inner surface of said shell for absorbing said microwave power, and a plurality of metallic contacts attached to said metallic shell, said metallic contacts being dimensioned to contact and extend fully across a section of inner wall surface of the waveguide transmission line to prevent arc-over and RF leakage.

8. The insertable waveguide load defined in claim 7 wherein means are provided at one end of said shell for facilitating the insertion and removal of said load from a section of the waveguide transmission line.

9. An insertable waveguide transmission line load for dissipating microwave power, said load comprising a hollow mould of lossy material having an entrance opening for receiving the microwave power, means for dissipating said microwave power by evenly distributing and absorbing said power through the walls of said lossy mould, a plurality of metallic contacts imbedded in said mould and outwardly a distance from the outer surface thereof, and means at one end of, said mould for facilitating the insertion and removal of said load from a section of the waveguide transmission line.

10. The waveguide transmission line load defined in claim 9 wherein the outer surface of said load is dimensioned to be insertable into the straight section of an antenna horn terminating said waveguide transmission line.

11. The waveguide transmission line load defined in claim 9 wherein flange means are provided on the outer end of said load for limiting the distance which said load can be inserted into said waveguide transmission line and for reducing radiation leakage therefrom.

12. A waveguide transmission line load for insertion into a section of waveguide tubing for dissipating microwave power, said load comprising a hollow mould of lossy material having an entrance opening for receiving microwave power, said entrance opening being provided with metallic strips for contecting the surface of the transmission line adjacent to said entrance opening and including a gently sloped portion for guiding said microwave power into said load with a minimum of discontinuity, means for dissipating said microwave power by evenly distributing and absorbing said power through the walls of said lossy mould, a plurality of metallic contacts imbedded in the outer portion of said lossy mould and extending a distance from the outer surface thereof, and a stop attached to the forward end of said lossy mould for limiting the travel of the load into the transmission line section.

13. An insertable waveguide transmission line load for dissipating microwave power, said load comprising a hollow metallic shell having an entrance opening for receiving microwave power, a coating of lossy material disposed on the inner surface of said shell for absorbing said microwave power, a plurality of metallic contacts attached to said metallic shell, said metallic contacts being dimensioned to contact and extend fully across a section of the inner wall surface of the waveguide transmission line, and sealing means including a flange member at the outer end of said load for preventing the escape of pressurized fluid while the microwave transmission line is in operation.

References Cited in the file of this patent UNITED STATES PATENTS 2,489,131 Hegbar Nov. 22, 1949 2,635,145 Luhurs Apr. 14, 1953 2,908,875 Blatt Oct. 13, 1959 FOREIGN PATENTS 494,181 Canada July 7, 1953 

